Vaccines have been used to prevent various diseases, and have provided tremendous and excellent results in the prevention of specific diseases such as smallpox. Nonetheless, vaccines also have side effects and there are many cases in which vaccines are less effective. Thus there is much room for improvement in the field of vaccines. Currently, many types of vaccines used for human or other animals are prepared by using pathogenic organisms, or parts thereof, as antigenic materials for vaccine production. This means that there is no denying the possibility that vaccines are contaminated with constituents of pathogenic organisms or ingredients of growth medium for pathogenic organisms. These contaminants can cause adverse side effects upon vaccination. In addition, antigenic sites associated with immunization themselves can induce side effects when inoculated in large quantity.
Attempts have been made to avoid such side effects as much as possible and to manufacture safe vaccines. Such attempts include the reduction of inoculum dose of vaccine, the use of high-purity preparations of antigen for vaccine, and the alteration of vaccination routes. However, these revisions have a general problem—the immunological activity of such revised vaccines tends to be reduced. Accordingly, adjuvants have been used to prevent such a decline of immunological activity. In such cases, there remain some problems to be solved, such as improvement in effectiveness and safety of adjuvants.
For example, a pathogenic microorganism such as influenza virus infects via mucous membranes. To prevent such diseases at early stages of infection, vaccines capable of significantly enhancing local immunity on the mucous membrane rather than systemic immunity in the blood are preferred. In this context, it is also preferable to have an adjuvant capable of contributing to the enhancement of local immunity. At the same time, instead of injection, oral, transdermal, or intranasal inoculation is noteworthy as a vaccination route. The injection must be performed by medical technicians and is, therefore, problematic when it is necessary to vaccinate many people under a condition with no or only poor medical facilities. In contrast, oral, transdermal, and intranasal inoculation can be performed without direct practices by medically skilled staffs, so long as vaccine preparations are available. In general, when vaccinated with an injectable vaccine, via alternate vaccination route, sufficient immunological stimulation is difficult to attain and, therefore, certain adjuvants suitable for alternate vaccination routes are needed.
In other words, an important challenge for the development of vaccines is to develop an excellent adjuvant that is effective and safe and that helps the enhancement of required immunity at the desired site.
Previously, aluminum compounds (aluminum sulfate, aluminum hydroxide, etc.) and phosphate compounds (calcium phosphate, aluminum phosphate, etc.) have widely been used as adjuvants for vaccination. Currently, the gel of these compounds is almost the only adjuvant that is used for human vaccination. However, there are some problems in regard to these adjuvants, and thus the adjuvants are in need of improvement. Some illustrations are as follows:
1) Problems associated with manufacturing and handling: For example, since the quality of these adjuvants tends to vary from one production lot to another, they are not suited to large-scale manufacturing. Moreover, the handling is also inconvenient. For example, they are unsuitable for column operation. 2) A problem associated with their effect: While they excel in inducing the humoral immunity, they are not effective for inducing the cellular immunity, and thus there are limitations on the types of antigens to be used.
Studies and development of new types of adjuvants, such as saponin, are proceeding in order to overcome the drawbacks. Some illustrations are as follows (See J. C. Cox et al., Vaccine 15, 248-256, 1997):    1. Surface active substances, such as saponins.    2. Bacterial toxins, such as cholera toxin.    3. Constituents of microorganisms or plants, such as BCG, and muramyl peptide.    4. Cytokines, such as interleukins.    5. Synthetic polyanion, polycation.    6. Micro-carriers.
The present inventors have found that certain extracts of Chinese and Japanese traditional (Kampo) medicine, consisting of several crude drugs, exhibit adjuvant activity and increase the antibody titer against influenza virus in the nasal irrigation liquid and in the serum when used as an ingredient of influenza vaccine to be inoculated intranasally (H. Yamada and T. Nagai, Methods and Findings in Experimental and Clinical Pharmacology, 20(3), 185-192, 1998). However, exactly which component(s) of the extract has the adjuvant activity remains to be clarified.